Error correcting typewriter

ABSTRACT

A typewriter, wherein an inked ribbon and an error correction ribbon are separately supported, separately fed and threaded through a single vibrator, is provided with an error correction key which operates on instrumentalities which condition the ribbon vibrator for movement to position the error correction ribbon opposite the printing line incident to typing a character, shifts the ribbon feed drive mechanism from the inked to the correction ribbon and conditions the carriage escapement controls to preclude operation of the escapement mechanism incident to typing a character whereby, with the typewriter carriage backspaced or moved to the position of an error and with the error key held depressed, an operator may type out the incorrect character, release the error key and type in the correct character.

United States Patent [191 Frechette et a].

[4 1 Sept; 16, 1975 ERROR CORRECTING TYPEWRITER [73] Assignee: Litton Business Systems, Inc., New

York, NY.

22 Filed: Feb. 22, 1974 21 App]. No.: 444,707

[52] US. Cl. 197/181; 197/151; 197/156; 197/168 [51] Int. Cl. B4lJ 29/16 [58] Field of Search 197/82, 83, 91, 97, 151, 197/156,l08,109,112,181,168

[56] References Cited UNITED STATES PATENTS 928,987 7/1909 Kunath 197/156 X 966,716 8/1910 Steele 197/156 1,030,500 6/1912 Brown 197/156 1,183,424 5/1916 Baldwin 197/181 3,149,711 9/1964 Wolowitz... 197/151 X 3,174,611 3/1965 LaP0inte.... 197/151 3,204,746 9/1965 Wolowitz". 197/181 X 3,397,767 8/1968 Hobbs 197/181 3,595,362 7/1971 Wolowitz... 197/181 X 3.598220 8/1971 McGrath.... 197/156 3,603,443 9/1971 McLean 197/156 3,604,549 9/1971 Caudill et a1. 197/151 3,724,633 4/1973 Korb etal 197/181 X 3,729,081 4/1973 Ozimek et al..... 197/181 X 3,747,734 7/1973 Norman et al.... 197/151 X 3,788,442 l/l974 Lehnhardt et a]. 197/151 X 3,799,316 3/1974 Davidge et al l97/9l X Primary ExaminerEdgar S. Burr Assistant Examiner-R. T. Rader Attorney, Agent, or FirmJoseph R. Spalla [5 7] ABSTRACT A typewriter, wherein an inked ribbon and an error correction ribbon are separately supported, separately fed and threaded through a single vibrator, is provided with an error correction key which operates on instrumentalities which condition the ribbon vibrator for movement to position the error correction ribbon opposite the printing line incident to typing a character, shifts the ribbon feed drive mechanism from the inked to the correction ribbon and conditions the carriage escapement controls to preclude operation of the escapement mechanism incident to typing a character whereby, with the typewriter carriage backspaced or moved to the position of an error and with the error key held depressed, an operator may type out the incorrect character, release the error key and type in the correct character.

9 Claims, 5 Drawing Figures PATENTED SEP '1 6 I975 SHiET 1 OF 9 PATENTED SE? 1 5 stain 2 0F 9 PATENTEB SEP 1 6 1975 ERROR CORRECTING TYPEWRITER This invention relates to typewriters or like business machines; more particularly, it relates to typewriters provided with an error correction ribbon operative to mask over or erase typing errors; and specifically, it relates to mechanisms associated with an error key and controlled thereby to switch ribbon drive to enable feed of the error correction ribbon, condition the ribbon elevating mechanism so that the error correction ribbon will be positioned opposite the writing line, and disable the escapement mechanism, all to facilitate correction of typed errors.

A number of error correcting typewriters employing separate inked and error correction ribbons with provision for selectively shifting ribbon drive from one to the other and for positioning the error correction ribbon are known in association with special keys which also control backspace mechansim and/or escapement disabling mechanisms. Exemplary prior art US. Pat. Nos. showing error correction typewriters employing two separate ribbon systems each with its own feed mechanism are the following:

Such known systems are either complicated in terms of mechansim or in terms of operator manipulation.

Accordingly, an object of the invention is to provide an error correction typewriting system which is relatively uncomplicated, easy for an operator to learn and less cumbersome to operate.

Another object of the invention is to provide a typewriter having inked and error correction ribbons sup ported therein and an error key to control operation of the error correction ribbon and preclude escapement to facilitate typing out errors and typing in correct characters.

Still another object of the invention is in the provision of a two ribbon error correction system in which an inked and an error correction ribbon track through a common ribbon elevating mechanism and wherein the error correction ribbon is made functional by controlling the throw of the ribbon elevating mechanism.

A further object of the invention is in the provision of error key controlled mechanism operatively associated with silent key mechanism to preclude escapement operation in error correction mode.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing in which like reference numerals designate like parts throughout the Figures thereof and wherein:

FIG. 1 is a perspective view of a type action and associated ribbon feed and escapement control mechanisms;

FIG. 2 is a perspective view showing an error key and associated connecting parts for conditioning the ribbon elevating mechanism for elevating the error correction FIGS..4 and S are views showing an exemplary cartridge mountable on the ribbon drive system of FIG. 3 containing ink and error correction ribbon supplies on opposite sides of the print point of the typewriter.

I Referring now to the drawing, there is shown in FIG. 1, a power operated type action including a type bar 10 pivoted as at 11 in a type bar supporting segment (not shown). The type bar 10 is connected by a link 12 to a sublever 13 which is pivoted on a fulcrum rod 14 transversely supported in machine side frames 15. An action return spring 16 is connected to a depending leg 17 of the sublever l3 and normally holds the sublever 13 and connected type bar 10 in a position of rest with the head 18 of the type bar 10 against a head rest (not shown). Pivotally mounted on the sublever 13 is an action drive cam 19 having a periphery of increasing radius which when rocked counterclockwise into engagement with a power roll 21 drives the sublever 13 and connected type bar 10 to strike a platen and print. The cam 19 is held rotatively biased out of engagement from the power roll 21 with its tail 22 against the depending leg 17 of the sublever 13 by a spring 23 extending between a second depending leg 24 of the sublever l3 and the cam 19. A trip lever 25 is pivoted on a transverse frame supported rod 26 forwardly of fulcrum rod 14 and has, as viewed in FIG. 1, a rearwardly extending leg 27 whose end 28 overlies a forward extension 29 of the cam 19. The trip lever 25 also has an upwardly extending leg 31 which bears against a key lever extension 32 under urge of a trip lever return spring 33 secured to leg 27 which also serves to restore a key lever 34 pivotally mounted on a key lever fulcrum 35. The sublever fulcrum rod 14 extends through and pivotally supports the legs 36L, 36R of an inverted U-shaped universal bar 37 which extends across the machine and is located in the path of an upward extension 38 of each sublever 13 whereby as a sublever 13 is driven counterclockwise, the U-bar 37 is rocked counterclockwise as viewed in FIG. 1 against return springs 37 The initial portion of the U-bar movement serves, through a guided link 39 which is pivotally attached to the left leg 36L of the U-bar 37 and which extends rearwardly, to move from the path of a lug 40 on the side of a ribbon feed roll cam 41 to permit a spring (not shown) to rock the cam 41 into engagement with the power roll 21 and be driven thereby thus to power operate a ribbon feed sublever 42 on which the cam 41 is eccentrically rotatably mounted. The ribbon feed sublever 42, also pivoted on the fulcrum rod 14 and biased to a rest position by a spring 42' is connected via a link 43 to a left ribbon drive crank 44 which is made fast on a transverse shaft 45 by means of a set screws through a boss 46 secured to the crank 44. The transverse shaft 45 which is rotatively supported in the machine side frames 15 extends across the machine and simultaneously operates a right ribbon drive crank 47 similarly secured thereto via a boss 46.

An escapement control link 48 is coupled to the right end of the U-bar 37 by way of an elongated slot 49 in a rearward extension 51 of the upper part of a link 36' secured to the right leg 36R of the U-bar 37 and a pin 52 secured to the escapement control link 48 operable to activate a well-known flying dog full drop escapement. Details of such a full drop escapement mechanism controlled by link 48 are shown in copending application of Theodore N. Madison Ser. No. 333,389, filed Feb. 16, 1973. In accordance with the invention,

an inverted silent U-bar 53 is also rotatably supported on fulcrum rod 14 with its legs 54 outwardly of the legs 36L, 36R of U-bar 37. As viewed in FIG. 1,.the righthand leg 54 of the silent U-bar 53 has a pin 55 which extends into a slot 56 of an escapement precluding link 57, pivotally supported on transverse shaft 45, which has a rearward extending arm 58 whose endis movable or interposable into the path of pin 52 of the escape rnent control link 48 to thereby block movement of the escapement control link 48 as well as. the terminal escapement controlling movement of the U- bar 37 whenever the silent U-bar 53 is operated as by a silent key action or an error key. A silent key action lever depression' against a silent U-bar return spring 53 secured to its right leg 54 will be associated with a sublever 13 whose upward extension 59 is longer as shown in dotted lines so as to rock the silent U-bar 53 together with the U-bar 37. As noted, the U-bar 37 by reason of slot 49 is allowed to move relative to pin 52 sufficiently to initiate a powered ribbon feed and allow a type bar to strike a platen to print prior to pulling the escapement control link 48 via pin 52 so as not to interfere with typing when pin 52 is blocked by interposition of arm 58.

to the error correction ribbon feed system, hereinafter described move the silent U-bar 53 to preclude an escapement incident to typing out an incorrect character, and setting the throw of a ribbon elevating means hereinafter described through which inked and error correction ribbons are trained so that the error correction ribbon will be elevated opposite the writing line incident to a type action. More particularly, there isshown in FIG. 2 a generally segment shaped bichrome selection lever 62 which is selectively positionable through an operator controlled link 63 to control the throw of the ribbon elevating means to effect printing through a black band of a composite ribbon, another color band of the composite ribbon, e.g., a red band, or to effect stencil typing. In accordance with the invention, the other color or red band position is assigned to error correction ribbon selection. The ribbon bichrome selection lever 62 is pivoted at its apex on a ribbon elevator control shaft 64 and is provided with detent slots 65 on its lower end 66 which cooperate with a detent 67 on the end of a flexible detent lever 68 to hold the bichrome selection lever arm in a selected position. Intermediate the pivot end and the detent end 66 of selection lever 62 is an elongated front to back curved slot 69 which receives and guides a pin 70 extending laterally from a link 71 connected to a lateral and upwardly directed extension 72 of the left leg 36L of U-bar 37 which extends through a slotL in the left machine side frame 15. The position of pin 70 along slot 69 determines the length of stroke imparted to ribbon elevating means generally designated by reference 73 in that it also extends into a slot 74 in a ribbon elevator crank 75 secured to the ribbon elevator control shaft 6.4 so that when the U-bar 37 is driven, the crank 75 is rocked and shaft 64 is turned to thereby raise the ribbon elevating means 73 by way of an eccentricportion 76 of shaft 64. The ribbon elevating means 73 which may take other forms comprises a pair of arms 73a' and 73b;

oted to arm 73a as at 73c. The arms 73a, 73b'are biased scissor fashion to open position by a spring 77 to the extend permitted by a slot 78 in a frame member 78. As shown in FIG. 2 the upper portion of each arm 73a, 73b narrows down in width'to formonthe outer edges there'of inclined camming surfaces 79. On elevation,

camming surfaces 79 in association with the edges of slot 78 forcethe arms 73a, 73b to close toward one another and positively engage aribbon elevator frame, hereinafter described for positive retraction as will hereinafter'appear with reference to FIG. 5.

The position of the ribbon bichrome selection lever 62 as stated above is also controlled by the error key lever 61 which is connected via a link 61' to a multiarmed crank 80 pivoted on the left machine side frame 15L. One arm 80a is connected by'a link 81 to a crank 82'(FIG. 2land FIG. 3) which is connected to a link 83 which effects a shift of ribbon feed drive from one to the other ribbon feed system 97,198 as hereinafter describedwith reference to FIG. 3.

With further reference to FIG. 2, another arm 84 on the multiarmed crank 80 operates against a pin 85 on a frame pivoted crank 86 which has an extension 87 operatively positioned to move the silent U-bar 53 to preclude an escapement inthe manner described in FIG. 1 incident to a type action. A still further arm 88 on the multiarmed crank 80 is connected by a link 89 to a twoarmed lever 91 pivoted on the left machine side frame 15L which when rocked causes its upper arm 92 to engage a pin 93 on the bichrome selection lever 62 to shift it to error correction ribbon position following engagement of its lower arm 94 with a lateral extension 95 of the detent lever 68 to thereby remove and hold out the detent 67 to permit the shift of the bichrome selection lever 62 to the error correction position. A spring 64a connected between pin 93 and an anchor 64b extending outwardly of the machine side frame 15L extends normally with its axis aligned with the center of shaft 64 when the parts are in the inked ribbon position shown and serves to restore lever 64 to the position illustrated when the error key lever 61 is re- I leased.

With reference to FIG. 3, there is shown mounted on spaced horizontal frame' plates 96L, 96R a left or inked ribbon feed 97 and a right or error correction ribbon feed system generally designated 98. Each system, distiriguished by the same reference numerals followed by L or R designating left and right, comprises a rotatably mounted ratchet 99 and a smaller diameter coaxial drive gear 101 which meshes with a driven capstan gear 102 which is employed in association with ribbon cartridge mounted gears 133, 134 (FIG. 5) to unidirectionally drive or pull associated. ribbons 47,119 from supplies which may be. mounted in receptacles 116, 118 (FIG. 4) ofa cartridge assembly 115 more particularlyxdescribed-with reference to FIG. 4 and FIG. 5, though other ribbon mountings are within the invention.

As shown in FIG. 3 there is mounted on each ratchet axis a right angled crank 103 connected as at 104 to the end of one arm 105 of a link l06'which is connected to the respective ribbon feed cranks 44 and 47. Pivoted "on the end of the other arm 107- of ribbon feed crank 103 is a feed pawl 108 urged by a spring 108 to engage and drive the ratchet 99. Each frame plate.96 also supports a' no back dog 109-also biased. by a spring. 109 into ratchet engagement. In addition, there is pivotally mounted on each base frame plate 96 as-at l 11, switching levers 1 12 which are linkedi'together tbya cross link 1 13. As shown in FIG. 3 of the-drawing,the leftxswitch= ing lever 112L is shown rocked counterclockwise about its pivot 111L withvan'extension 114L thereof holding the left feed pawl l08ls-out'o'f ratchet engagement. In this position, the right switching lever-112Ris also in its counterclockwise rocked position'allowing the right feed pawl 108R to engage its ratchet99Rl With reference to FIGS. 4--and 5,-an exemplary form of replaceable-ribbon supports'tructure adapted for operation with the drivesystem of FIG.- 3- is shown,it being understood that other ribbon drive systems and ribbon support arrangements are within-the iirvention. More particularly, the ribbon-support'structure comprises a cartridge assembly 115' including a'left receptacle 116 which rotatably supports a spool of error' correction ribbon 117 and a right receptacle 118-which r'otatably supports a spool ofinked ribbon. e;g.-, carbon ribbon 119 at a vertically spaced level. The cartridge 115 is further defined by a'rearhollow bridge member 121 and a front bridge member 122 in'the'fo'rm 'of spaced vertical walls -122a,'1'22b which-guide membetween the inked 119 and correction 117ribbo n one above the other in their passage past the machine print point 123. The hear wall 122a of the front bridgemrnber 122 is provided with bent out ears 124 which embrace and locate the cartridge assembly 115 on the machine type guide 125 (FIG. As best seen in FIG. 5, the walls 1220, 122b of the front bridge member 122 opposite the print point 123 of the typewriter are provided with openings defining a rectangular window 126. A ribbon elevator frame 127 comprising vertical arms 128 spaced on either side of the print point 123 is slidably supported in the window 126 by four lugs 129 which extend laterally between the spaced vertical walls 122a, 12217 of the front bridge member 122. Each vertical arm 128 is channeled to provide ribbon passage 1280 therethrough as shown in the magnified portion of FIG. 4. The elevator frame 127 has a recess 130 in its lower joined end which is downwardly open to freely receive and be supported by the upper ends of elevating arms 73a 73b which are releasably coupled thereto incident to elevating movment by reason of the relative movement of arms 73a and 73b toward one another to a position where the overhangs 131 of the elevating arms 73a, 73b move over the shelves 132 formed by the restricted opening to the recess 130.

As shown in FIG. 4, each receptacle 116, 118 supports gear wheels 133, 134 which when the cartridge assembly 115 is loaded on the drive system of FIG. 3 will be in operative driving engagement with an associated drive capstan gear 102 and when driven thereby will pull ribbon 117, 119 between gear wheels 133 and 134.

As viewed in F IG. 5, each receptacle 116, 118 has an upper and lower compartment 135 and 136 and in accordance with the invention the inked ribbon supply spool 119 is housed in the upper compartment 135 of the right receptacle 118 and the error correction ribbon supply spool 117 is housed in the lower compartment 136 of the left receptacle 1 16. The geared wheels 133 and 134 in the right receptacle 118, located in the lower compartment 136, will pull used error correction ribbon 117 to the right where it will be stored in the lower compartment 136 thereof, while used carbon ribbon 119 will be pulled by the gear wheels 133, 134 located in the upper compartment 135 of the left receptacle-r116 and stored in theupper'compartmen't 135 thereofi; :5 m w Wherethe inked ribbon is a fabric ribbon-which 'receives more than one time use;ai'su'jiiply of randomly folded-'tendle'ss" fabric; rribbonf is 'hou'sed-"in the upper compartment 135 of the-"left receptacle 116. and the fabric is pulled past the printing point 123 from compartment 135 through-the irear lio'llow bridge' l2l through the upper compartment 1350f the'right receptacle around a ribbon 'guide :139.- I

I In operation, when an error or errors 'are sensed by antoper'ator, the machine'carriage is moved either manually or-vthroug'h backspace operations to present the incorrect character opposite the printing point 123. The operator then depresses the error key lever 61 which through link 89 shifts the bichror'ne selection lever 62 to condition the ribbonelevating means 73 for a higher stroke incident to the next typ'ed character, shifts, through link 81, the'r'ibbon feed from the left rib-,

bon feed ratchet 96L to the right feed ratchet R as- U-bar'53 to prevent arr-escapement operation'incident to 'typing'out the incorrect characterfi After depressing the erro 'r' key lever'61 and whileholdin'g it down, the incorrect character will be'typed through the error correction" ribbon 1'17 and erased. On release of the error correction key lever 61," the parts will be rest position and the correct character may be typed through the inked ribbon 119.

The invention claimed is: l. A typewriter having key controlled means for typing characters at a relatively movable print point,

a unidirectional inked ribbon drive, a unidirectinal error correction ribbon drive, a single ribbon elevating means, means for supporting an error correction ribbon and an inked ribbon for driving engagement with associated ribbon drives and for movement past said print point through said single ribbon elevating means,

means for enabling one and disabling the other of said ribbon drives to move either said error correction ribbon or said inked ribbon past said print point incident to typing,

said ribbon elevating means including throw selecting means positionable to condition either said inked ribbon or said error correction ribbon for elevation in front of said print point incident to typing,

escapement control means operative incident to and following typing,

interposer means for precluding, when positioned,

operation of said escapement control means,

an error key lever,

and error key lever controlled mechanism operative, when and for as long as said error key lever is held depressed, on said means for enabling one and disabling the other of said ribbon drives to enable the error correction ribbon drive and disable the inked ribbon drive, to position throw selecting means to condition said error correction ribbon for elevation opposite said print point incident to typing, and to position said interposer means to preclude operation of said escapement control means incident to typing.

2. A typewriter as recited in claim 1, including a universal bar rockable incident to typing,

and means responsive to rocking of said universal bar 7. for indexing the' enabled one of said ribbon drives.

3. A typewriter as recited in claim 2, including means responsive to rocking of said universal bar for elevating said ribbon elevating means.

4. A typewriter as recited in claim 1, said escapement control means including a universal bar rockable incident to typing,

a first control link coupled to-said universal bar,

said coupling comprising a pin on said control link extending into a slot on said universal bar,

said pin and slot coupling effecting movement of said control link to effect an escapement after typing, and said interposer means for precluding operation of said escapement control means comprising an interponent movable into the path of said pin.

5. A typewriter as recited in claim 4, said interposer means including a silent universal bar rockable incident to typing silent characters or incident to error key depression, sand said interponent being connected to said silent universal bar.

6. A typewriter as recited in claim 1, said inked ribbon drive and said error correction ribbon drive each comprising a ratchet and a drive pawl spring urged into engagement therewith, means for swinging said pawls to rotate said ratchets incident to typing, and means normally disabling said error correction ribbon drive pawl from engagement with its associated ratchet and enabling engagement of the. inked ribbon drive pawl with its associated ratchet, said last named means being swtichable incident to depression of said error key lever to enable said error correction ribbon drive pawl and disable said inked ribbon drive pawl.

7. A typewriter as recited in claim 1, said ribbon drives being supported on opposite sides of said print point for moving said inked and error correction ribbons in opposite directions.

8. A typewriter as recited in claim 1, said ribbons being supported for movement in vertically spaced tracks.

9. In a typewriter as recited in claim 1, said key controlled means including, a sublever connected to drive a type bar and operable in response to depression of an associated key lever, a first universal bar located in the path of movement of said sublever and movable thereby to operate said escapement control means after said type bar has printed, said interposer means including a second universal bar having an interponent positionable on movement of said second universal bar to block the movement of said first universal baar to preclude operation of said escapement control means, said error key lever controlled mechanism moving said second universal bar to position said interponent on depression of said error key lever.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,905,465

DATED I September 16, 1975 lN\/ ENTOR(S) 3 Thomas E. Frechette and Daniel J. Rosborg It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In The Specification:

Column 3, lines l3, l4 and 15, after "action" (second occurrence) delete lever depression against a silient U-bar return spring 53' secured to its right leg 54"; line 13, after "key" (first occurrence) insert --lever depression against a silent U-bar return spring 53' secured to its right leg 54--; line 26, change "swtich" to -switch--; line 28, after "described" insert a comma line 48, change "arm" to --62--; line 54, change "15L" to -l5'-; line 55, change "15" to l5L--.

Column 4, line 2, change "tend" to --tent-; line l8, change "system" to --systems--; line 52, change 47" to --ll7-.

Column 5, line 25, change "hear" to -rear--; line 38, change "sage" to --sages--.

Column 6, line 27, after "be" insert --restored to--.

In The Claims:

Claim 1, line 4, change "unidirectinal" to --unidirectional-; line 29, after "position" insert --the--.

Claim 5, line 4, change "sand" to --and- Claim 9, line 10, change "baar" to -bar--.

Signed and Scaled this third Day Of February 1976 [SEAL] Arrest:

RUTH'C. M X SON C. MARSHALL DANN Arresrmg Officer Commissioner uflatents and Trademarks 

1. A typewriter having key controlled means for typing characters at a relatively movable print point, a unidirectional inked ribbon drive, a unidirectinal error correction ribbon drive, a single ribbon elevating means, means for supporting an error correction ribbon and an inked ribbon for driving engagement with associated ribbon drives and for movement past said print point through said single ribbon elevating means, means for enabling one and disabling the other of said ribbon drives to move either said error correction ribbon or said inked ribbon past said print point incident to typing, said ribbon elevating means including throw selecting means positionable to condition either said inked ribbon or said error correction ribbon for elevation in front of said print point incident to typing, escapement control means operative incident to and following typing, interposer means for precluding, when positioned, operation of said escapement control means, an error key lever, and error key lever controlled mechanism operative, when and for as long as said error key lever is held depressed, on said means for enabling one and disabling the other of said ribbon drives to enable the error correction ribbon drive and disable the inked ribbon drive, to position throw selecting means to condition said error correction ribbon for elevation opposite said print point incident to typing, and to position said interposer means to preclude operation of said escapement control means incident to typing.
 2. A typewriter as recited in claim 1, including a universal bar rockable incident to typing, and means responsive to rocking of said universal bar for indexing the enabled one of said ribbon drives.
 3. A typewriter as recited in claim 2, including means responsive to rocking of said universal bar for elevating said ribbon elevating means.
 4. A typewriter as recited in claim 1, said escapement control means including a universal bar rockable incident to typing, a first control link coupled to said universal bar, said coupling comprising a pin on said control link extending into a slot on said universal bar, said pin and slot coupling effecting movement of said control link to effect an escapement after typing, and said interposer means for precluding operation of said escapement control means comprising an interponent movable into the path of said pin.
 5. A typewriter as recited in claim 4, said interposer means including a silent universal bar rockable incident to typing silent characters or incident to error key depression, sand said interponent being connected to said silent universal bar.
 6. A typewriter as recited in claim 1, said inked ribbon drive and said error correction ribbon drive each comprising a ratchet and a drive pawl spring urged into engagement therewith, means for swinging said pawls to rotate said ratchets incident to typing, and means normally disabling said error correction ribbon drive pawl from engagement with its associated ratChet and enabling engagement of the inked ribbon drive pawl with its associated ratchet, said last named means being swtichable incident to depression of said error key lever to enable said error correction ribbon drive pawl and disable said inked ribbon drive pawl.
 7. A typewriter as recited in claim 1, said ribbon drives being supported on opposite sides of said print point for moving said inked and error correction ribbons in opposite directions.
 8. A typewriter as recited in claim 1, said ribbons being supported for movement in vertically spaced tracks.
 9. In a typewriter as recited in claim 1, said key controlled means including, a sublever connected to drive a type bar and operable in response to depression of an associated key lever, a first universal bar located in the path of movement of said sublever and movable thereby to operate said escapement control means after said type bar has printed, said interposer means including a second universal bar having an interponent positionable on movement of said second universal bar to block the movement of said first universal baar to preclude operation of said escapement control means, said error key lever controlled mechanism moving said second universal bar to position said interponent on depression of said error key lever. 